Childhood obesity is a growing concern. We and others have evidence that dairy consumption is associated with moderation of body weight and body fat. Whether this effect is due to calcium alone or to other constituents in dairy is unclear. We propose to test the hypothesis that increased calcium intake through salts or dairy products increases fecal fat excretion as a result of intestinal soap formation, thereby reducing metabolizable energy intake. Dairy product consumption has also been associated with an increase in thermic effect of feeding and increased lipid oxidation, which would increase total energy expenditure. We hypothesize that increased calcium intake through salts or dairy products will increase total energy expenditure by increasing lipid oxidation and thermic effect of feeding and that these effects will be associated with a suppression of serum parathyroid hormone (PTH) and calcitriol concentrations. We will study these putative mechanisms in 30 overweight to moderately obese adolescent girls and boys who participate in two, three-week strictly controlled diet periods in a randomized order, crossover design. All subjects will receive a basal diet containing 650 mg calcium/day. Calcium intake and source will be manipulated through beverages consumed 3 times daily. During one period, the beverage will provide no additional calcium. During the other period, the beverage will provide an additional 650 mg calcium/day as calcium carbonate in half of the subjects or dairy calcium in the other half of the subjects. Balance (intake-excreta) will be determined for fat, energy, calcium and protein (nitrogen). Total energy expenditure will be determined using doubly labeled water and resting energy expenditure and the thermic effect of feeding will be determined using indirect calorimetry. This study will evaluate calcium/dairy as a modulator of energy balance, important to the management of body fat in children.